As for now, we have addressed the basis tone of the guitars, as expected on a record. We have seen how compression, saturation and filters allow creating a guitar sound which is compatible with what our ear is used to get. But this sound must be located in the 3D space: that's where delays, echoes, reverbs and stereo chorus have a role to play.

As a matter of fact, the guitar is only a part of the band, and all the instruments cannot be located at the same place:

Point 1: Some instruments are far away, others are close to you.

Point 2: Some instruments are on the left, some instruments are on the right.

Point 3: We assume that all the instruments are place on a horizontal plan...

This physical distribution was natural when music was always played live, with acoustic instruments. But rock music is played by electric instruments, with two main situations: on stage, or via a record. In both situations, the sound flows from two speakers, not from the individual location of each instrument.

Let's address first the far/close control issue. The stereo question will be addressed in the next section.

Remember that the speed of sound is slow: around 300m/s. A drummer located 6 meters behind the other instruments will be heard 20ms after the rest of the band…Imagine a test configuration where the drum track would go through a 100ms delay (one shot, no repeat, only the delayed sound). It would be equivalent to a drummer located 30m behind the band. That’s a beginning. Just a silly test, that allows finding the right solution. In the real life, a plain one shot delay is not sufficient to give the feeling of distance: it helps, but it’s not enough. In fact, we would just think that the drummer is late on the beat…

Instead of a delay, let’s add some reverb to the drum sound. A reverb doesn’t repeat the sound: it adds a sort of decay after the original end of the sound. During this decay, we get a complex combination of what we’ve just heard. This combination is a complex sum of micro-delays that can have an average value of, let’s say 30ms. 30ms correspond to a distance of 10m. Got it? A sound with reverb will be heard with a feeling of distance!
Adding reverb to a sound is one of the tricks that can provide a distance feeling. Echo chambers (or delays now) can be used in a similar manner, usually with repeated echoes.

Reverb and echo are very old effects now: they can be achieved via electro-mechanic means, and reverb is originally a natural effect that any large hall can provide. They belong to the “time-based” effects family, a term which covers now other effects such as flanging and chorus.

With Boston, Tom Scholz has used almost every possible delay, echo and reverb technique. In the Rockman line, entirely based on solid-state analog technology, all these echo& reverb processors are based on Bucket-Brigade Delay (BBD) chips. These components, available since 1975, allowed developing fine delay units and acceptable reverbs, but also allowed creating the modern flangers and chorus effects.